Dyalog is historically Windows-based and .Net is the preferred solution for a lot of things. But it has reasonable support for most of what you mention. There's a solid FFI, and text is UTF-32 internally with support for I/O with other encodings. See the list of system functions at [0]. Conga is the http library but I don't have any idea how well it works.

This is an area where array languages are entirely different from one another. J and K have been using shebangs for a long time (although J does this by assuming a shebang will be valid but no-op code, and fails if the path contains a space… sigh). Support for interop just depends on what other applications are considered important by the developers of that particular language.

[0] https://help.dyalog.com/18.2/#Language/System%20Functions/Su...